The invention relates to a method for momentarily identifying a gas or a fluid, or a composition thereof, with the help of a sensing device such as mass-flow sensor.
Here, `the composition` is understood to refer to quality, but especially to quantity; in which concentration a specific component is present in a gas (mixture), statically, but also dynamically `in the time`. Concentrations may change, e.g., by altering additions of the substance in question. Thus, data are obtained on the course of the composition in question; the extent to which it changes: to wit: `on line`. Such data are of importance for various processes; e.g., in the semiconductor industry where, for certain processes, such as Chemical Vapour Deposition--CVD--, it is necessary to keep the concentration of the reaction-gas, which causes films of a material to precipitate onto a substrate, as constant as possible.
On-line measurements (i.e., measurements during the process) of the said type are not carried out as yet; data on, e.g., the concentration, are `calculated back` from the result and then fed back to the device by which said concentrations are controlled, such as in a CVD process where the `bubbler`, by means of which a reaction-gas is fed to a carrier-gas.